The present invention relates generally to stirring methods and apparatus and more particularly to turbulent stirring units which achieve highly efficient mixing.
Magnetic stirring plates for stirring of fluid in a vessel are known in the prior art where a stirring element in the form of a permanent bar magnet is placed in the fluid and rotated by means of an externally applied rotating magnetic field. According to such a method, the stirring element may be rotated without direct physical contact by means of an external rotating magnet.
In the past, magnetic stirrers have been designed and constructed so that the stirring motion produces a vortex whose center is coincident with the axis of rotation. While generally satisfactory, such stirrers have several disadvantages. Once the vortex is established, mixing is quit limited unless the speed is sufficient to cause vortex turbulence. Such turbulence is usually undesirable. This reduction in mixing once the vortex is formed is contrary to the desired goal of an efficient mixing which would achieve rapid and uniform distribution throughout the volume of the fluid.
Other types of "contactless" stirring devices in which this disadvantage is overcome are known. An example of such a prior art device used to achieve a more efficient mixing is the vortex stirrer used in serology. Such a device consists essentially of a surface rotating at constant speed with which a test tube or such held lightly in an operator's hand may be brought into contact, thus rotating the test tube. When a vortex is created, the operator removes the test tube slightly from the rotating surface, causing the vortex to collapse. By repeatedly creating and collapsing the vortex, a fairly efficient mixing is rapidly achieved. Such an operation, however, requires human intervention, is limited to small volumes and is fairly tedious. By application of the principles of the present turbulent stirring unit, operation of the vortex stirrer may be completely mechanized while retaining its high mixing efficiency.
An object of the present invention, therefore, is to provide a stirring method and apparatus for improving the rapidity and effectiveness of mixing.
A further object of the present invention is to provide such an apparatus that operates automatically without human intervention.
Another object of the present invention is to provide such a method according to which numerous processes may be either independently or identically controlled.